Oppdaget i 1956 av Chien-Shiung Wu i det som nå er kjent som [The Wu experiment](https://en.wikipedia.org/wiki/Wu_experiment). Fra [David Tong's Simulation Lecture](https://www.youtube.com/watch?v=QPMn7SuiHP8): > She took a bunch of cobolt nuclei, and she watched them die. So, she took cobolt nuclei in an excited state, and when the nuclei decayed, she discovered that they emitted electrons (which was known anyway), but, importantly, they emitted electrons in exactly the same direction (preferentially, this is quantum mechanics so everything is a bit random), but preferentially they emitted electrons in the same direction that the nuclei were spinning (per the right hand rule). (...) So in a mathematical sense what Wu discovered is that the symmetry of *parity*, of looking in a mirror, is *not* respected by the laws of physics.